Path Computation Element Method to Support Routing and Wavelength Assignment in Wavelength Switched Optical Networks

ABSTRACT

A network component comprising at least one processor configured to implement a method comprising transmitting a request to compute a routing assignment, a wavelength assignment, or both, wherein the request comprises a lightpath constraint indicator is disclosed. Also disclosed is an apparatus comprising a Path Computation Client (PCC) configured to transmit a request to and receive a reply from a Path Computation Element (PCE), wherein the request comprises a lightpath constraint, and wherein the reply comprises a routing assignment, a wavelength assignment, an error message, a no-path indication, or combinations thereof. Included is a method comprising receiving a request comprising a request parameter (RP) object comprising a lightpath constraint, sending a reply comprising a routing assignment, a wavelength assignment, an error message, a no-path indicator, or combinations thereof, wherein the request is received and the reply is sent using path computation element protocol (PCEP).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/173,873, filed Jul. 16, 2008 by Lee, et al. and entitled “PathComputation Element Method to Support Routing and Wavelength Assignmentin Wavelength Switched Optical Networks,” which claims priority to U.S.Provisional Patent Application No. 60/983,022 filed Oct. 26, 2007 by Leeet al. and entitled “Path Computation Element Method to Support Routingand Wavelength Assignment in Wavelength Switched Optical Networks,” bothof which are incorporated herein by reference as if reproduced in theirentireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Wavelength division multiplexing (WDM) is one technology that isenvisioned to increase bandwidth capability and enable bidirectionalcommunications in optical networks. In WDM networks, multiple datasignals can be transmitted simultaneously between network elements (NEs)using a single fiber. Specifically, the individual signals may beassigned different transmission wavelengths so that they do notinterfere or collide with each other. The path that the signal takesthrough the network is referred to as the lightpath. One type of WDMnetwork, a wavelength switched optical network (WSON), seeks to switchthe optical signals with fewer optical-electrical-optical (OEO)conversions along the lightpath, e.g. at the individual NEs, thanexisting optical networks.

One of the challenges in implementing WDM networks is the determinationof the routing and wavelength assignment (RWA) for the various signalsthat are being transported through the network at any given time. Unliketraditional circuit-switched and connection-oriented packet-switchednetworks that merely have to determine a route for the data streamacross the network, WDM networks are burdened with the additionalconstraint of having to ensure that the same wavelength is notsimultaneously used by two signals over a single fiber. This constraintis compounded by the fact that WDM networks typically use specificoptical bands comprising a finite number of usable optical wavelengths.As such, the RWA continues to be one of the challenges in implementingWDM technology in optical networks.

SUMMARY

In one embodiment, the disclosure includes a network componentcomprising at least one processor configured to implement a methodcomprising transmitting a request to compute a routing assignment, awavelength assignment, or both, wherein the request comprises alightpath constraint indicator.

In another embodiment, the disclosure includes an apparatus comprising aPath Computation Client (PCC) configured to transmit a request to andreceive a reply from a Path Computation Element (PCE), wherein therequest comprises a lightpath constraint, and wherein the replycomprises a routing assignment, a wavelength assignment, an errormessage, a no-path indication, or combinations thereof.

In yet another embodiment, the disclosure includes a method comprisingreceiving a request comprising a request parameter (RP) objectcomprising a lightpath constraint, sending a reply comprising a routingassignment, a wavelength assignment, an error message, a no-pathindicator, or combinations thereof, wherein the request is received andthe reply is sent using path computation element protocol (PCEP).

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a WSON system.

FIG. 2 is a protocol diagram of an embodiment of the communicationsbetween a PCE and a PCC.

FIG. 3 is a schematic diagram of an embodiment of a PCE architecture.

FIG. 4 is a schematic diagram of another embodiment of the PCEarchitecture.

FIG. 5 is a schematic diagram of another embodiment of the PCEarchitecture.

FIG. 6 is a schematic diagram of an embodiment of a request parameter(RP) object.

FIG. 7A is a schematic diagram of an embodiment of a lightpath routeparameter Type-Length-Value (TLV).

FIG. 7B is a schematic diagram of an embodiment of a lightpath routeparameter object.

FIG. 8 is a schematic diagram of an embodiment of a tuning range TLV.

FIG. 9 is a schematic diagram of an embodiment of a wavelength selectionpreference TLV.

FIG. 10 is a schematic diagram of an embodiment of an objective functionTLV.

FIG. 11 is a schematic diagram of an embodiment of a no path object.

FIG. 12 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Disclosed herein is a system and method for extending PCEP toaccommodate RWA in WDM networks, such as the WSON. Specifically, a PCCmay send a request to a PCE using PCEP. The request may include varioustypes of lightpath constraints, such as a RWA computation option, aroute parameter, a wavelength selection preference, an optimizationdegree, a timeliness characteristic, a duration, or combinationsthereof. The lightpath constraints may be used in the computation of theRWA, and the RWA may be returned to the PCC using a PCEP reply.Alternatively, the PCEP reply may contain an error message or no pathindicator if the RWA cannot be computed.

FIG. 1 illustrates one embodiment of a WSON system 100. The system 100may comprise a WSON 110, a control plane controller 120, and a PCE 130.The WSON 110, control plane controller 120, and PCE 130 may communicatewith each other via optical, electrical, or wireless means. The WSON 110may comprise a plurality of NEs 112 coupled to one another using opticalfibers. In an embodiment, the optical fibers may also be considered NEs112. The optical signals may be transported through the WSON 110 overlightpaths that may pass through some of the NEs 112. In addition, someof the NEs 112, for example those at the ends of the WSON 110, may beconfigured to convert between electrical signals from external sourcesand the optical signals used in the WSON 110. Although four NEs 112 areshown in the WSON 110, the WSON 110 may comprise any number of NEs 112.

The WSON 110 may be any optical network that uses active or passivecomponents to transport optical signals. The WSON 110 may implement WDMto transport the optical signals through the WSON 110, and may comprisevarious optical components as described in detail below. The WSON 110may be part of a long haul network, a metropolitan network, or aresidential access network.

The NEs 112 may be any devices or components that transport signalsthrough the WSON 110. In an embodiment, the NEs 112 consist essentiallyof optical processing components, such as line ports, add ports, dropports, transmitters, receivers, amplifiers, optical taps, and so forth,and do not contain any electrical processing components. Alternatively,the NEs 112 may comprise a combination of optical processing componentsand electrical processing components. At least some of the NEs 112 maybe configured with wavelength converters, optical-electrical (OE)converters, electrical-optical (EO) converters, OEO converters, orcombinations thereof. However, it may be advantageous for at least someof the NEs 112 to lack such converters as such may reduce the cost andcomplexity of the WSON 110. In specific embodiments, the NEs 112 maycomprise optical cross connects (OXCs), photonic cross connects (PXCs),type I or type II reconfigurable optical add/drop multiplexers (ROADMs),wavelength selective switches (WSSs), fixed optical add/dropmultiplexers (FOADMs), or combinations thereof.

The NEs 112 may be coupled to each other via optical fibers. The opticalfibers may be used to establish optical links and transport the opticalsignals between the NEs 112. The optical fibers may comprise standardsingle mode fibers (SMFs) as defined in ITU-T standard G.652, dispersionshifted SMFs as defined in ITU-T standard G.653, cut-off shifted SMFs asdefined in ITU-T standard G.654, non-zero dispersion shifted SMFs asdefined in ITU-T standard G.655, wideband non-zero dispersion shiftedSMFs as defined in ITU-T standard G.656, or combinations thereof. Thesefiber types may be differentiated by their optical impairmentcharacteristics, such as attenuation, chromatic dispersion, polarizationmode dispersion, four wave mixing, or combinations thereof. Theseeffects may be dependent upon wavelength, channel spacing, input powerlevel, or combinations thereof. The optical fibers may be used totransport WDM signals, such as course WDM (CWDM) signals as defined inITU-T G.694.2 or dense WDM (DWDM) signals as defined in ITU-T G.694.1.All of the standards described herein are incorporated herein byreference.

The control plane controller 120 may coordinate activities within theWSON 110. Specifically, the control plane controller 120 may receiveoptical connection requests and provide lightpath signaling to the WSON110 via Generalized Multi-Protocol Label Switching (GMPLS), therebycoordinating the NEs 112 such that data signals are routed through theWSON 110 with little or no contention. In addition, the control planecontroller 120 may communicate with the PCE 130 using PCEP, provide thePCE 130 with information that may be used for the RWA, receive the RWAfrom the PCE 130, and/or forward the RWA to the NEs 112. The controlplane controller 120 may be located in a component outside of the WSON110, such as an external server, or may be located in a component withinthe WSON 110, such as a NE 112.

The PCE 130 may perform all or part of the RWA for the WSON system 100.Specifically, the PCE 130 may receive the wavelength or otherinformation that may be used for the RWA from the control planecontroller 120, from the NEs 112, or both. The PCE 130 may process theinformation to obtain the RWA, for example, by computing the routes,e.g. lightpaths, for the optical signals, specifying the opticalwavelengths that are used for each lightpath, and determining the NEs112 along the lightpath at which the optical signal should be convertedto an electrical signal or a different wavelength. The RWA may includeat least one route for each incoming signal and at least one wavelengthassociated with each route. The PCE 130 may then send all or part of theRWA information to the control plane controller 120 or directly to theNEs 112. To assist the PCE 130 in this process, the PCE 130 may comprisea global traffic-engineering database (TED), a RWA information database,an optical performance monitor (OPM), a physical layer constraint (PLC)information database, or combinations thereof. The PCE 130 may belocated in a component outside of the WSON 110, such as an externalserver, or may be located in a component within the WSON 110, such as aNE 112.

In some embodiments, the RWA information may be sent to the PCE 130 by apath computation client (PCC). The PCC may be any client applicationrequesting a path computation to be performed by the PCE 130. The PCCmay also be any network component that makes such a request, such as thecontrol plane controller 120, or any NE 112, such as a ROADM or a FOADM.

FIG. 2 illustrates an embodiment of a path computation communicationmethod 200 between the PCC and the PCE. The method 200 may beimplemented using any suitable protocol, such as the PCEP. In the method200, the PCC may send a path computation request 202 to the PCE. Therequest may include any of the lightpath constraints disclosed below. At204, the PCE calculates a path through the network that meets thelightpath constraints. For example, the PCE may calculate the RWA. ThePCE may then send a path computation reply 206 to the PCC. The reply 206may comprise the RWA or one of the other reply options described below.

When a network comprises a plurality of PCEs, not all PCEs within thenetwork may have the ability to calculate the RWA. Therefore, thenetwork may comprise a discovery mechanism that allows the PCC todetermine the PCE in which to send the request 202. For example, thediscovery mechanism may comprise an advertisement from a PCC for aRWA-capable PCE, and a response from the PCEs indicating whether theyare RWA-capable. The discovery mechanism may be implemented as part ofthe method 200 or as a separate process.

The PCE may be embodied in one of several architectures. FIG. 3illustrates an embodiment of a combined RWA architecture 300. In thecombined RWA architecture 300, the PCC 310 communicates the RWA requestand the required information to the PCE 320, which implements both therouting assignment and the wavelength assignment functions using asingle computation entity, such as a processor. For example, theprocessor may process the RWA information using a single or multiplealgorithms to compute the lightpaths as well as to assign the opticalwavelengths for each lightpath. The amount of RWA information needed bythe PCE 320 to compute the RWA may vary depending on the algorithm used.If desired, the PCE 320 may not compute the RWA until sufficient networklinks are established between the NEs or when sufficient RWA informationabout the NEs and the network topology is provided. The combined RWAarchitecture 300 may be preferable for network optimization, smallerWSONs, or both.

FIG. 4 illustrates an embodiment of a separated RWA architecture 400. Inthe separated RWA architecture 400, the PCC 410 communicates the RWArequest and the required information to the PCE 420, which implementsboth the routing function and the wavelength assignment function usingseparate computation entities, such as processors 422 and 424.Alternatively, the separated RWA architecture 400 may comprise twoseparate PCEs 420 each comprising one of the processors 422 and 424.Implementing routing assignment and wavelength assignment separately mayoffload some of the computational burden on the processors 422 and 424and reduce the processing time. In an embodiment, the PCC 410 may beaware of the presence of only one of two processors 422, 424 (or twoPCEs) and may only communicate with that processor 422, 424 (or PCE).For example, the PCC 410 may send the RWA information to the processor422, which may compute the lightpath routes and forward the routingassignment to the processor 424 where the wavelength assignments areperformed. The RWA may then be passed back to the processor 422 and thento the PCC 410. Such an embodiment may also be reversed such that thePCC 410 communicates with the processor 424 instead of the processor422.

In either architecture 300 or 400, the PCC may receive a route from thesource to destination along with the wavelengths, e.g. GMPLS generalizedlabels, to be used along portions of the path. The GMPLS signalingsupports an explicit route object (ERO). Within an ERO, an ERO labelsub-object can be used to indicate the wavelength to be used at aparticular NE. In cases where the local label map approach is used, thelabel sub-object entry in the ERO may have to be translated.

FIG. 5 illustrates a distributed wavelength assignment architecture 500.In the distributed wavelength assignment architecture 500, the PCE 510may receive some or all of the RWA information from the NEs 520, 530,and 540, perhaps via direct link, and implements the routing assignment.The PCE 510 then directly or indirectly passes the routing assignment tothe individual NEs 520, 530, and 540, which assign the wavelengths atthe local links between the NEs 520, 530, and 540 based on localinformation. Specifically, the NE 520 may receive local RWA informationfrom the NEs 530 and 540 and send some or all of the RWA information tothe PCE 510. The PCE 510 may compute the lightpaths using the receivedRWA information and send the list of lightpaths to the NE 520. The NE520 may use the list of lightpaths to identify the NE 530 as the next NEin the lightpath. The NE 520 may establish a link to the NE 530 and usethe received local RWA information that may comprise additionalconstraints to assign a wavelength for transmission over the link. TheNE 530 may receive the list of lightpaths from the NE 520, use the listof lightpaths to identify the NE 540 as the next NE in the lightpath,establish a link to the NE 540, and assign the same or a differentwavelength for transmission over the link. Thus, the signals may berouted and the wavelengths may be assigned in a distributed mannerbetween the remaining NEs in the network. Assigning the wavelengths atthe individual NEs may reduce the amount of RWA information that has tobe sent to the PCE 510.

As mentioned above, the request may comprise at least one lightpathconstraint. The lightpath constraint may be any parameter that affectsor limits the use of wavelengths along the lightpaths within thenetwork. In an embodiment, the lightpath constraints may include a RWAcomputation option. The RWA computation option may specify the portionsof the RWA that needs to be solved or otherwise considered. Suitable RWAcomputation options include routing assignment, wavelength assignment,routing and wavelength assignment, and routing assignment with asuggested or restricted wavelength set. Routing assignment may indicatethat the NE desires the routing assignment, but not the wavelengthassignment. Alternatively, routing assignment may indicate that therouting assignment is separated from the wavelength assignment, asindicated in FIG. 4 above. In either case, the request may also comprisethe wavelength assignment. Wavelength assignment may indicate that theNE desires the routing assignment, but not the wavelength assignment.Alternatively, wavelength assignment may indicate that the wavelengthassignment is separated from the routing assignment, as indicated inFIG. 4 above. In either case, the request may also comprise the routingassignment. Routing and wavelength assignment may indicate that the NEdesires both the routing assignment and the wavelength assignment or amore optimal RWA. Finally, routing assignment with a suggested orrestricted wavelength set may indicate that the NE desires the routingassignment and a suggested or restricted set of wavelengths such ascandidate wavelengths from which the NE may select the wavelengths toassign to the lightpath(s). Alternatively, routing assignment with asuggested or restricted wavelength set may indicate that the wavelengthassignment is distributed, as indicated in FIG. 5 above.

In a specific embodiment, the RWA computation option may be included ina request parameter (RP) object in the request. FIG. 6 illustrates oneembodiment of a suitable RP object 600. The RP object 600 may include areserved field 602, which is reserved for other purposes and maycomprise the first about 9 bits of the RP object 600. The RP object 600may also comprise a flags field 610 that may indicate various types ofdata and may comprise the subsequent about 23 bits. For example, the RWAcomputation option may be embodied as a RWA Computation (RC) flag 614located in the flags field 610 of the RP object 600. The RC flag 614 maybe about 2 bits in length and may be defined as indicated in Table 1below.

TABLE 1 Bit Description 00 Routing Assignment 01 Wavelength Assignment10 Routing Assignment with Suggested or Restricted Wavelength Set 11Routing and Wavelength AssignmentAlternatively, the RC flag 614 may be set to 01 to indicate wavelengthassignment, 10 to indicate routing assignment, or 11 to indicate routingand wavelength assignment. FIG. 6 illustrates that the RP object 600 mayalso include any one or more of a directionality (I) 612 flag, abidirectional (B) flag 616, or both. The I flag 612 and the B flag 616are discussed below, while the remaining flags are described by theInternet Engineering Task Force (IETF) PCE Working Group Internet Draftsand Requests for Comments (RFCs), which are available atwww.ietf.org/html.charters/pce-charter.html. The RP object 600 may alsoinclude a Request ID Number 620, which may be a unique identifierassociated with the RP object 600. The RP object 610 may also includeone or more optional TLVs 630 or objects such as the various TLVs andobjects described below. As used herein, the terms “TLV” and “object”may both refer to any data structure that conveys any part or theentirety of a lightpath constraint.

In an embodiment, the lightpath constraints may include a routeparameter. The route parameter may indicate a limitation in theassignment of wavelengths to the lightpath. Suitable route parameteroptions include bidirectional assignment of wavelengths, simultaneousassignment of wavelengths to a primary lightpath and a backup lightpath,and optical transmitter tuning range constraints. Bidirectionalassignment of wavelengths may indicate that a single wavelength shouldbe assigned to a lightpath and used for two-way communications or thatseparate wavelengths should be assigned to each direction of thelightpath. Simultaneous assignment of wavelengths to a primary lightpathand a backup lightpath may indicate that the same wavelength should beassigned to the primary lightpath and the backup lightpath.Alternatively, simultaneous assignment of wavelengths to a primarylightpath and a backup lightpath may indicate that separate wavelengthsshould be assigned to the primary lightpath and the backup lightpath.The optical transmitter tuning range constraint may indicate thewavelengths at which any optical transmitters along the lightpath cantransmit.

In an embodiment, the RP object may indicate the route parameter.Specifically, the flags field 610 may include a bidirectional (B) flag616, which may be about 1 bit in length in length. When the B flag 616is set to zero, the request may be for a unidirectional TrafficEngineered Label Switched Path (TE LSP). When the B flag 616 may be setto one, the request is for a bidirectional TE LSP. When the B flag 616is set to one, the flags field 610 may include a directionality (I) flag612, which may comprise about 1 bit within the flags field 610. The Iflag 612 may indicate the request is for a bidirectional wavelengthassignment when set to one. The I flag 612 may indicate the request isfor a unidirectional wavelength assignment when set to zero.

In a specific embodiment, the route parameter may be included in alightpath route parameter (LRP) TLV, also known as a RP object, in therequest. For example, when the RC flag described above indicates one ofthe three options comprising wavelength assignment, an optional LRPobject, such as the LRP TLV, may be included with the RP object. FIG. 7Aillustrates one embodiment of a suitable LRP TLV 700. The LRP TLV 700may include a type field 702, a length field 704, and a value field 706.The type field 702 may comprise the first about 16 bits of the TLV 700,and may indicate that the LRP TLV 700 is a route parameter TLV. Thelength field 704 may be the subsequent about 16 bits of the LRP TLV 700,and may indicate the length of the value field 706. The value field 706may be any size, but in some embodiments is the subsequent about 32 bitson the LRP TLV 700 and may indicate the route parameter. In anembodiment, the value field 706 is about 2 bits in length and maycomprise a bidirectional (I) flag 708 and a same wavelength (S) flag710. Alternatively, the value field 706 may be about one bit in lengthand may comprise the S flag 710. The I flag 708 may be about 1 bit inlength, and may indicate the directionality of the wavelengthassignment. For example, the LRP TLV 700 may indicate a bidirectionalassignment of wavelengths when the I flag 708 is set to zero, and theLRP TLV 700 may indicate a unidirectional assignment of wavelengths whenthe I flag 708 is set to one. Similarly, the S flag 710 may be about 1bit in length, and may indicate the commonality of the wavelengthassignment. For example, the LRP TLV 700 may indicate an assignment ofthe same wavelength to the upstream direction and the downstreamdirection when the S flag 710 is set to zero, and the TLV 700 mayindicate an assignment of different wavelengths to the upstreamdirection and the downstream direction when the S flag 710 is set toone.

In an embodiment, the lightpath constraints may include a timelinesscharacteristic. The timeliness characteristic may indicate theimportance of timeliness to the request or how quickly the RWA should becalculated. Suitable optimization degree options include time critical,soft time bounds, and scheduled. Time critical may indicate thattimeliness is important to the request, and may typically be used forrestoration of network services or for other high-priority real-timeservice requests. Soft time bounds may indicate that timeliness is ofmoderate importance to the request. Soft time bound requests should behandled in a responsive manner, but may allow sufficient time for someamount of network optimization. Soft time bounds may typically be usedfor new or first-time connection requests. Scheduled may indicate thattimeliness is not overly important to the request. Scheduled requestsmay be used for services requested prior to receipt of the signal, andmay receive the highest degree of network optimization.

In an embodiment illustrated by FIG. 7B, a LRP object 750 may beincluded as a part of the request. The LRP object 750 may include areserved field 752, which may be the first about 9 bits and may be usedfor other purposes. The LRP object 750 may also include a flags field760, which may be the subsequent about 23 bits and may indicate varioustypes of data. The flags field 760 may comprise a timelinesscharacteristic (TC) flag 762, which may be about 2 bits in length. TheTC flag 762 may indicate the timeliness characteristic is time criticalwhen the TC flag 762 is set to 11, the timeliness characteristic is softtime bounds when the TC flag 762 is set to 10, or the timelinesscharacteristic is scheduled when the TC flag 762 is set to 01. The LRPobject 750 may also include a Request ID Number 770, which may be aunique identifier associated with the LRP object 750. The LRP object 750may also include one or more optional TLVs or objects 780.

In a specific embodiment, the flags field 760 may also include anidentical wavelength (I) flag 764 and a bidirectional (B) flag 766. TheI flag 764 may be about 1 bit in length, and may indicate the assignmentof an identical wavelength to a primary and a backup path. For example,the I flag 764 may indicate the assignment of an identical wavelength toa primary and a backup path when set to one, and the I flag 764 mayindicate the assignment of different wavelengths to the primary and thebackup path when set to zero. Similarly, the B flag 766 may be about 1bit in length, and may indicate the commonality of the wavelengthassignment. For example, the B flag 766 may indicate a bidirectionalassignment of wavelengths when set to one, and the B flag 766 mayindicate a unidirectional assignment of wavelengths when set to zero.

In an embodiment, the LRP object may include an optional transmittertuning range TLV. FIG. 8 illustrates one embodiment of a suitabletransmitter tuning range TLV 800. The TLV 800 may include a type field802, a length field 804, and a value field 810. The type field 802 maycomprise the first about 7 bits of the TLV 800, and may indicate thatthe TLV 800 is a tuning range TLV. The length field 804 may be variablein size, but in some embodiments may be the subsequent about 7 bits ofthe TLV 800, and may indicate the length of the value field 810. Thevalue fields 810 may be any size, but in some embodiments is thelatter-most about 64 bits of the TLV 800 and may indicate a lower bound806 and an upper bound 808 for the transmitter tuning range.

In an embodiment, the lightpath constraints may include a wavelengthselection preference. The wavelength selection preference may indicatethe criteria by which the wavelength assignment is assigned to thelightpath. Suitable wavelength selection preference options includerandom, first fit, most used, least loaded, and no preference. Randommay indicate that the wavelength should be randomly chosen from a groupof suitable wavelengths. First fit may indicate that the wavelengthshould be the first suitable wavelength that is found. Most used mayindicate that the selected wavelength should be the most commonly usedwavelength within the group of all suitable wavelengths. Least loadedmay indicate that the selected wavelength should be the least commonlyused wavelength within the group of all suitable wavelengths. Finally,no preference may indicate that the PCC does not care or has no opinionas to the selected wavelength assignment.

In a specific embodiment, the wavelength selection preference may beincluded in a wavelength selection preference object in the request. Forexample, when the RC flag in the RP object described above indicates oneof the three options comprising wavelength assignment, an optionalwavelength selection preference object, such as a wavelength TLV, may beincluded with the RP object. FIG. 9 illustrates one embodiment of asuitable wavelength selection preference TLV 900. The TLV 900 mayinclude a type field 902, a length field 904, and a value field 906. Thetype field 902 may comprise the first about 16 bits of the TLV 900, andmay indicate that the TLV 900 is a wavelength selection TLV 900. Thelength field 904 may be the subsequent about 16 bits of the TLV 900, andmay indicate the length of the value field 906. The value field 906 maybe any size, but in some embodiments is the subsequent about 32 bits ofthe TLV 900 and may comprise a function code. The function code mayindicate the wavelength selection preference as indicated in Table 2below.

TABLE 2 Function Code Wavelength Selection Preference 1 Random 2 FirstFit 3 Most Used 4 Least Loaded 5 No Preference

In a specific embodiment, the objective function may be included in anobjective function object in the request. The objective function mayspecify the reason for or objective when implementing the routingassignment, wavelength assignment, or both. For example, when the RCflag in the RP object described above indicates one of the optionscomprising wavelength assignment, an optional objective function object,such as an objective function TLV, may be included with the RP object.FIG. 10 illustrates one embodiment of a suitable objective function TLV1000. The TLV 1000 may include a type field 1002, a length field 1004,and a value field 1006. The type field 1002 may comprise the first about16 bits of the TLV 1000, and may indicate that the TLV 1000 is awavelength selection TLV 1000. The length field 1004 may be thesubsequent about 16 bits of the TLV 1000, and may indicate the length ofthe value field 1006. The value field 1006 may be any size, but in someembodiments is the subsequent about 32 bits of the TLV 1000 and maycomprise a function code. The function code may indicate the objectivefunction as indicated in Table 3 below.

TABLE 3 Function Code Wavelength Selection Preference 1 Reduce orminimize the total number of links and/or wavelengths used 2 Reduce orminimize the maximum links and/or wavelengths used (load balance) 3Reduce or minimize the path length of all flows

In an embodiment, the lightpath constraints may include an optimizationdegree. The optimization degree may indicate the number of lightpathsthat are included in a single RWA calculation. Suitable optimizationdegree options include concurrent optimization, simultaneous request ofa primary lightpath and a backup lightpath, or sequential optimization.Concurrent optimization may indicate that multiple lightpaths arecontained in a single request. Simultaneous request of a primarylightpath and a backup lightpath may indicate that two lightpaths arerequested: a primary lightpath that is intended to carry the signal, anda backup lightpath that can carry the signal if the primary lightpathfails. The primary and the backup lightpaths may have completelydifferent routes, some common portions of their routes, or the sameroute. Similarly, the primary and the backup lightpaths may usecompletely different wavelengths, some common wavelengths if the networkcomprises at least one converter, or the same wavelength. While theprimary and backup lightpaths may share some or all of their routing andwavelength assignment, the primary and backup lightpaths generally donot have the exact same routing and wavelength assignment. If desired,the request may indicate whether the primary and backup lightpaths areto share routing assignment, wavelength assignment, or both, as well asthe extent of such. Sequential optimization may indicate that a singlelightpath is contained in the request.

In an embodiment, the lightpath constraints may include a duration. Theduration may indicate the length of the time in which the signal will bein service. Suitable duration options include dynamic, pseudo-static,and static. Dynamic may indicate that the signal will last a relativelyshort amount of time. Pseudo-static may indicate that the signal willlast a moderate amount of time. Static may indicate that the signal willlast a relatively long time.

After the request comprising the lightpath constraint has been receivedby the PCE, the PCE may issue a reply back to the PCC. The reply mayinclude the RWA computed subject to the lightpath constraints indicatedabove. In addition, the reply may include any or all of the lightpathconstraints that were contained in the request. If there is no RWA thatsatisfies the lightpath constraints, the reply may indicate such, forexample using a no path indicator. Additionally or alternatively, thereply may indicate which parts of the RWA could not be obtained. Forexample, the reply may indicate that a suitable route could not befound, a suitable wavelength could not be found, or a suitablecombination of a route and a wavelength could not be found. Finally, thereply may include a suggestion for relaxing the lightpath constraints toobtain the RWA. For example, if the RWA would have been obtainable butfor the presence of one lightpath constraint, e.g. duration, then thereply may indicate such.

In a specific embodiment, the indication that RWA could not be obtained,any suggestions for relaxation of the lightpath constraints, or anycombination thereof may be included in a no path object as illustratedby FIG. 11. The no path object 1100 may include a reserved field 1120about 8 bits in length, which may be used for other purposes. Theno-path object 1100 may also include a Nature of Issue (NI) field 1102,which comprises the first 8 bits of the no path object 1100. The NIfield 1102 may indicate the nature of the issue that resulted in the RWAnot being obtained. For example, a value equal to eight (0x08) mayindicate that no path satisfying the set of constraints could be found.Similarly, a value equal to ten (0x10) may indicate that no wavelengthwas found associated with the RWA computation in the PC Reply message.

In a specific embodiment, a no path object 1100 may also include a flagsfield 1110 that may be about 16 bits in length. The flags field 1110 maycomprise a plurality of flags. For example, the flags field 1110 maycomprise an unsatisfied constraints (C) flag 1112 that may be about 1bit in length and may indicate the reasons why a path could not befound. For example, the C flag 1112 indicates a set of unsatisfiedconstrains when the C flag 1112 is set to one. When the flag is set tozero, the C flag 1012 indicates no reason why a path could not be found.

In yet another embodiment, the no path object 1100 may include one ormore optional TLVs 1130. For example, the no path object 1100 mayinclude a no path vector TLV in the no path object 1100. For example, a0x10 bit flag may be set to one in the no path vector TLV to indicatethat no route, wavelength, or both was found that satisfied thelightpath constraints in the request. In another example, a 0x08 bitflag may indicate that no path was found.

In an embodiment, the reply may include at least one message. Forexample, if the PCE is not configured to calculate a RWA, then the replymay contain an error message that the PCE is not configured to calculatethe RWA. Such an error message may contain a PCEP error object and anerror-value, such as error-type=15 and the error-value=1. Alternatively,if the request is not compliant with administrative privileges, then thereply may contain an error message that indicates that the request isnot compliant with administrative privileges. Such an error message maycontain a PCEP-error object and an error-value, such as the error-type=6and the error-value=3. Further in the alternative, if the request or theRWA violates some policy within the PCE or the WSON, then the reply maycontain an error message that indicates the policy violation. Such anerror message may contain a PCEP error object, such as error-type=6. Inany event, the request may be cancelled, and a new request may have tobe sent to the PCE.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 12 illustrates a typical, general-purpose networkcomponent 1200 suitable for implementing one or more embodiments of thecomponents disclosed herein. The network component 1200 includes aprocessor 1202 (which may be referred to as a central processor unit orCPU) that is in communication with memory devices including secondarystorage 1204, read only memory (ROM) 1206, random access memory (RAM)1208, input/output (I/O) devices 1210, and network connectivity devices1212. The processor 1202 may be implemented as one or more CPU chips, ormay be part of one or more application specific integrated circuits(ASICs).

The secondary storage 1204 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 1208 is not large enough tohold all working data. Secondary storage 1204 may be used to storeprograms that are loaded into RAM 1208 when such programs are selectedfor execution. The ROM 1206 is used to store instructions and perhapsdata that are read during program execution. ROM 1206 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 1204. The RAM 1208 is usedto store volatile data and perhaps to store instructions. Access to bothROM 1206 and RAM 1208 is typically faster than to secondary storage1204.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1. An apparatus comprising: a Path Computation Client (PCC) configuredto transmit a Path Computation Element (PCE) Protocol (PCEP) request(PCReq) message to a PCE, wherein the PCReq message comprises a routingand wavelength assignment (RWA) computation option comprising a pathcomputation type indicator that specifies whether the PCReq message isrequesting both routing and wavelength assignment or routing only. 2.The apparatus of claim 1, wherein if the path computation type indicatorindicates that the PCReq message is requesting routing only, thendistributed wavelength assignment is performed at each node of a route.3. The apparatus of claim 1, wherein if the path computation typeindicator indicates that the PCReq message is requesting both routingand wavelength assignment, then the PCReq message indicates use ofexplicit route labels for wavelength assignments.
 4. The apparatus ofclaim 1, wherein if the path computation type indicator indicates thatthe PCReq message is requesting both routing and wavelength assignment,then the PCC is further configured to receive a PCEP reply (PCRep)message that includes a route, a wavelength assigned to the route, and awavelength assignment option that has been applied.
 5. The apparatus ofclaim 1, wherein the PCC is further configured to receive a PCEP reply(PCRep) message that indicates why a valid path was not found.
 6. Theapparatus of claim 5, wherein the PCRep message indicates that a validpath was not found because there was no route that satisfied alllightpath constraints.
 7. The apparatus of claim 5, wherein the PCRepmessage indicates that a valid path was not found because there was nowavelength that satisfied a wavelength range constraint.
 8. Theapparatus of claim 2, wherein the PCReq message comprises a bulk requestfor simultaneous computation of multiple lightpaths specified in anumber of RWA path requests.
 9. The apparatus of claim 8, wherein thePCC is further configured to receive a PCEP reply (PCRep) message thatincludes a route and a wavelength assigned to the route for each RWApath request specified in the original PCReq message.
 10. The apparatusof claim 2, wherein the PCReq message indicates whether the pathcomputation request is for a more optimal RWA.
 11. The apparatus ofclaim 2, wherein if the path computation type indicator indicates thatthe PCReq message is requesting wavelength assignment, then the PCReqmessage further comprises a wavelength range constraint that specifies arestriction on the wavelengths to be used.
 12. The apparatus of claim 2,wherein the PCReq message specifies preferences or constraints forwavelength assignments (WA) that include random assignment, most used(descending order), or least used (ascending order).
 13. A wavelengthswitched optical network (WSON) architecture for supporting routing andwavelength assignment (RWA) comprising: a Path Computation Element (PCE)configured to receive a PCE Protocol (PCEP) request (PCReq) message froma Path Computation Client (PCC) over an RWA PCC to PCE interface,wherein the PCReq message comprises an RWA computation option comprisinga path computation type indicator that specifies whether the PCReqmessage is requesting both routing and wavelength assignment or routingonly.
 14. The WSON architecture of claim 13 further comprising aplurality of nodes posited along a computed route, wherein if the pathcomputation type indicator indicates routing only, then distributedwavelength assignment is performed at each node along the route.
 15. TheWSON architecture of claim 13, wherein the PCE is further configured tosend a PCEP reply (PCRep) message that indicates a route, a wavelengthassigned to the route, and a wavelength assignment option that has beenapplied.
 16. The WSON architecture of claim 13, wherein if the PCE isunable to compute a valid path, then the PCE is further configured tosend a PCEP reply (PCRep) message that indicates why a valid path wasnot found.
 17. The WSON architecture of claim 13, wherein the PCReqmessage comprises a bulk request for simultaneous computation ofmultiple lightpaths specified in a number of RWA path requests, andwherein the PCE is further configured to send a PCEP reply (PCRep)message comprising a route and a wavelength assigned to the route foreach RWA path request specified in the original PCReq message.
 18. Amethod comprising: transmitting a request to compute a routingassignment, a wavelength assignment, or both, wherein the requestcomprises a lightpath constraint indicator and a request parameter (RP)object, wherein the lightpath constraint indicator comprises a routingand wavelength assignment computation (RC) flag in the RP object, andwherein the RC flag selectively indicates a path computation typerelated to the request to be both routing and wavelength assignment(RWA) or to be routing only.
 19. The method of claim 18, wherein the RCflag indicates: a routing assignment and a wavelength assignment whenthe RC flag is set to a first value, the wavelength assignment but notthe routing assignment when the RC flag is set to a second value, therouting assignment with a suggested wavelength set or a restrictedwavelength set when the RC flag is set to a third value, or the routingassignment but not the wavelength assignment when the RC flag is set toa fourth value.
 20. The method of claim 18, wherein the RC flagcomprises a two bit flag field.